Certainly for a model 1987X from 2006 and probably other recent models.
To save cutting small holes in the front fascia, to take the pot ant-rotation lugs, they've cut them off and then not even secured the pots with star washers under the bush nuts or fascia. So even in careful useage the nuts work loose in a couple of years which is fine inside an electric quitar , just a rat's nest of knotted signal wires, no elf 'n safety issue there. But not for valve amps - needs a modification to stop each of the pots rotating and then bare connections touching.
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on
Irrelevant probably. As long as there's no shock risk to the user, it's fine.
I am a fairly experienced safety (and EMC) 'expert' btw. Ilearnt from some of the best. Since around 1987. You might say it makes the product unreliable ? Nought to do with safety.
I was quite wondering just how Mr Cook was intending to 'modify' the mounting of pots - if the anti rotation peg is broken off, surely he`s going to have to replace all the pots, and drill the panel to accept the peg. Either that, or bodge something up? Either way I can`t see the proud owner of a nice new Marshall amp being too chuffed about it being modified from box standard in any way.
If you must know, replace plain washers with spring washers to reduce chance of nuts slackening in the first place.
The 1mm tinned copper wire earth strap soldered to and across each pot is not enough to stop, wire breaking and the pots rotating.
If in an electric guitar I replace the wire with flat copper strip, soldered to each pot case, the sort of enamelled high current wire used in some power transformers, with the enamelling stripped off.. In these sorts of cases, not wishing to add to any electrical hazard, 3/8 wide cable-tie with the fastener cut off , bridging the back of each pot, and then 1/8 inch cable ties around each pot and the wide nylon.
If the owner does not like the appearance of such on the INSIDE of his amp, FFS , well he can cut them off himself. But I am obliged to make some sort of remedial works.
Traditional chassis mounted pots ie with loose wiring, not loomed, not pcb mount ones.
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on
But I am obliged to make some sort of remedial works.
Personally, I dont think you are. Whilst I might agree with you about the spring washers, modifying the construction method of an item of kit which has already passed whatever required regulations, could in my view leave you open to liability if something goes pearshaped in the future.
What say you Graham, you know a lot more about this than me?
Well if my car came back from Kwik Fit with all sorts of extra wires and ties holding the exhaust on "better", I'd wonder WTF the fitter thought he was doing, and how much he had charged me for the priviledge.
I'm somewhere in between. Given a real issue with future reliability, I appreciate the attention paid. OTOH, it's a sales job for the technician as to the utility of such modification.
Many, many guitars (and other kit--I like that particularly British term) do indeed exhibit the loose pot--and loose jakc--syndrome. Most experienced players carry tools to tighten the nuts, forestalling or eliminating future failure...and consider it to be just another part of regular maintenance--like adjusting the bridge or filing frets. Less experienced players either have not seen the problem, or if so, believe it to be an issue with their particular instrument. They are the ones who would benefit most, and be hardest to sell.
As for the Marshall amp, again, many bought the unit on the strength of reputation. They're possibly not ever going to use it enough for the issue to exhibit. Those who do will either believe their case to be unique, or at least unusual. Pros will either appreciate the fix, or move on to more reliable brands (or more solidly constructed vintage originals).
So, I see the issue as a sales job. Unlike my vehicle (I look under mine regularly, but how many people do?), the mods made by Mr. Cook are only going to manifest in the absence of future problems, or in the telling by him. He'll either have to justify the extra expense, or simply absorb it.
As to the actual fix, all those outlined sound viable to me. I think I'd go for a multi-pronged approach. In fact using all of them is not without merit for a unit which needs to be bullet-proof in daily professional use--and these are the customers who will appreciate (and pay for) the extra attention. Additionally, a 'chemical' solution seems indicated. Applying a thread locking compound to the nuts would help. 'Painting' the nut to the shaft and panel with something like fingernail polish is an effective, simple fix which requires no removal of the actual pot hardware...adding little shop time for the tech to justify the expense of.
These amps have a printed plastic finnish covering over the fascia metal. With a thread lock chemical approach the plastic can still compress under the bush nuts ,microscopically, plus metal creep and soon the pots will turn if the knob is rotated to either endstop.
The anti-rotation lugs are there for chassis mount ring tagged and wired pots precisely to stop any chance of rotation - up until the point is reached when the the pot has fallen off , that is.
If the wiring was loomed and laced tight it would be a reasonably satisfactory alternative .
Kit and kaboodle is the full term but I don't know what a kaboodle is or was.
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on
So, say you were non-techie and someone was repairing your vintage Gibson noticed that some of the rubber insulation over the HT or mains wiring was perished and cracking off - you would say oh that's fine its of no consequence, leave it, as its original. ?
I see nothing intrinsically wrong with the vintage bods who remove the wrappers from ancient leaky paper capacitors, sorry condensers, and replace with modern functional polypropylene ones covered with the original wrapper. But safety matters are something else.
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on
I`d put the star washers on the inside - metal to metal - and lock with varnish or glue also on the inside. I use pva adhesive as it holds fast, is slightly flexible so doesnt crack yet can be easily removed if need be.
If you're determined to stop the pots rotating, how about soldering a length of stiff copper wire right along the tops of all the pots, directly to the cases? that`s often done any way to bond them all together.
Kit meaning equipment comes from kitbag. caboodle means property
Well, firstly Gibson guitars don`t have much in the way of mains or HT wiring.
However say it was a vintage amplifier I was repairing, of course I would replace defective wiring with new, but I`d try to keep it in the spirit of the original, I certainly wouldn`t chop and change it around on my own personal whim or paranoia.
Indeed, some guys will happily pay for you to go to the trouble of reusing the old condenser casing and carefully fitting new caps inside. I did a WEM Copycat some time ago in such a fashion with those yellow and red caps and I have a fair stock of the old Mullard brown blobs. When rewiring say, a Stratocaster the customer wants the same varnished cotton covered black and white wire as original. I've even heard of someone making dummy replica 'death caps'for those US ampss!
It`s important to some people that it looks as original as possible inside and out.
I repair a LOT of Marshalls. I can't remember ever seeing a pot that has been turned around on its mounting. Plenty that have got bashed from the front or the shaft broken off, and possibly some that have actually been turned with too much force, and the pot has disintegrated internally instead.
Sure, make something better where it is appropriate, and with the appropriate skills and method, which I often do. Lashing a whole bunch of pots with a whole bunch of cable ties does not fit in with my version of appropriate. Sound more like some over enthusiastic bodging. I would not be pleased to see that on my amp, car, bicycle, chimney stack, cat, etc.
We see a lot of poor design these days, but I think in the end, we just have to live with it. Today, for instance, I had a 'modern' version of the Vox AC15 on the bench. For a start, you can't even get at the output valves, without removing the chassis, so that's not too clever for 'on the road' maintenance for a start. The problem with this particular amp was that the sound was very 'thin', and there was a substantial amount of hum continuously present. When I had the chassis out, it was clear that one of the output valves was seriously distressed, with its anode glowing red hot. I reached for my meter and probed the control grid pin on the affected valve, and the wire just fell off. These are chassis mounted valve bases, with wires going back to the nearby pcb, and what sort of wire have they used ? Thin single strand, about like telephone extension wire. The wire had neatly broken just at the end of the insulation.
Now I know these Voxs are built in China now under license, but they are designed in the UK for goodness sake. Who in their right mind, would use thin rigid single strand wire in a bit of kit that is going to be bounced around on the road as part of its normal natural working life ? And what on earth was the designer's team leader thinking of, when he signed off on this to production ? I think that the inaccessibility of the output valves, and the use of this type of wire for internal hookups, are both inexcusable design errors, and not the sort of thing that serious users would be expecting from a (formerly) reputable name like Vox. The wiring issue is a good example of what *could* be done by a service engineer to improve future reliability. He could replace all of those flying wires to the valve sockets with multistrand ones, but should he ? Would it be worth it ? Would the owner appreciate and pay for it ? I think I'm with everyone else on this one, and the answer is "no" on all three counts ...
Current capacity's probably all right. The Chinamen probably nicked it with the strippers. That said, stranded would be more reliable. As to the tubes being inside...that's just wrong. Does it say 'No user replaceable parts inside. Refer all servicing to qualified personnel'?
Doing that--especially if the entire unit is 'questionable'--is not always proper. Well, it's 'proper' in the sense that it's the right way to repair something; but improper if the client is not willing to pay for the bench time. On most gear the cost would exceed the value of the finished product. As a business, you can't afford to re-engineer every piece of gear that comes across your bench, at your own expense.
Better to fix the obvious problems, explain that it may reoccur and hand it back...or forgo any repair at all. With just about *everything* these days being engineered to the bottom line, you've just hit on the reason for the demise of the local repair shop.
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